x1, y1 = 2.3, 2.5
x2, y2 = 6.4, 3.1
x3, y3 = 5.1, 7.2
print((x1 * y2 + x2 * y3 + x3 * y1 - x1 * y3 - x2 * y1 - x3 * y2) / 2)
